这是什么C ++函数声明

Question

Im new to C++ and what im working on the docs tell me to look at the example code only it doesnt explain anything so im trying to decipher it.

i came a across this declaration of a function but i dont fully understand it.

just the first function

i get underneath part what i dont get is after the MHWRender::MPxShaderOverride(obj) and then it starts as a list of arguments(or what its called i dont know)

and i guess where i would find what the specified inputs would be.

again i have no idea what this is doing so im a bit lost in how to explain it.

full code can be found here: http://help.autodesk.com/view/MAYAUL/2016/ENU/?guid=__cpp_ref_hw_phong_shader_2hw_phong_shader_8cpp_example_html

    hwPhongShaderOverride(const MObject& obj)
: MHWRender::MPxShaderOverride(obj)
, fShaderNode(NULL)
, fTextureData(NULL)
, fDrawUsingShader(true) // Disabling this will use fixed-function which only has an OpenGL implementation
, fShaderBound(false)
, fTexture(NULL)
, fInColorPass(false)
, fColorShaderInstance(NULL)
, fInShadowPass(false)
, fShadowShaderInstance(NULL)
, fTransparency(0.0f)
{
    // Create a shader instance to use for drawing
    //
    if (fDrawUsingShader)
    {
        createShaderInstance();
    }
    fAmbient[0] = fAmbient[1] = fAmbient[2] = 0.0f;
    fDiffuse[0] = fDiffuse[1] = fDiffuse[2] = fDiffuse[3] = 0.0f;
    fSpecular[0] = fSpecular[1] = fSpecular[2] = 0.0f;
    fShininess[0] = fShininess[1] = fShininess[2] = 500.0f;
}

// override blend state when there is blending
static const MHWRender::MBlendState *sBlendState;

// Current hwPhongShader node associated with the shader override.
// Updated during doDG() time.
hwPhongShader *fShaderNode;
// Shader inputs values including transparency
float fTransparency;
float fAmbient[3];
float fDiffuse[4];
float fSpecular[3];
float fShininess[3];

// Temporary system buffer for creating textures
unsigned char* fTextureData;

// Pass tracking
bool fInColorPass;
bool fInShadowPass;

// Draw with texture or shader flag
bool fDrawUsingShader;
// VP2 texture
MHWRender::MTexture *fTexture;
// VP2 color shader
MHWRender::MShaderInstance *fColorShaderInstance;
// VP2 shadow shader
MHWRender::MShaderInstance *fShadowShaderInstance;
mutable bool fShaderBound;

Answer 1

This is a class constructor. The class is named hwPhongShaderOverrideMObject , and it derives from MHWRender::MPxShaderOverride , eg:

class hwPhongShaderOverrideMObject : public MHWRender::MPxShaderOverride
{
    ...
};

hwPhongShaderOverride(const MObject& obj) specifies that this constructor takes one argument as input, a const reference to a MObject instance. The constructor is being declared and implemented inline inside the class declaration itself, rather than being implemented separately from its declaration. Both approaches are allowed in C++.

Everything between : and { is the initialization list for the constructor. It initializes members of the class.

: begins the initialization list.

MHWRender::MPxShaderOverride(obj) is passing the input object to the base class constructor. Base classes must always be constructed first.

, fShaderNode(NULL) is initializing the fShaderNode member to NULL.

, fTextureData(NULL) is initializing the fTextureData member to NULL.

And so on until { is reached to end the initialization list. Then the body of the constructor is entered, like any other function, after the class members have been initialized first.

Answer 2

Below is a constructor.

hwPhongShaderOverride(const MObject& obj)
: MHWRender::MPxShaderOverride(obj)
, fShaderNode(NULL)
, fTextureData(NULL)
, fDrawUsingShader(true) // Disabling this will use fixed-function which only has an OpenGL implementation
, fShaderBound(false)
, fTexture(NULL)
, fInColorPass(false)
, fColorShaderInstance(NULL)
, fInShadowPass(false)
, fShadowShaderInstance(NULL)
, fTransparency(0.0f)
{
    // Create a shader instance to use for drawing
    //
    if (fDrawUsingShader)
    {
        createShaderInstance();
    }
    fAmbient[0] = fAmbient[1] = fAmbient[2] = 0.0f;
    fDiffuse[0] = fDiffuse[1] = fDiffuse[2] = fDiffuse[3] = 0.0f;
    fSpecular[0] = fSpecular[1] = fSpecular[2] = 0.0f;
    fShininess[0] = fShininess[1] = fShininess[2] = 500.0f;
}

It is using an initializer list to initialize its member variables by calling their constructors. hwPhongShaderOverride inherits from MHWRender::MPxShaderOverride , so it calls MHWRender::MPxShaderOverride 's constructor as the first element in the initializer list (ie, MHWRender::MPxShaderOverride(obj) .

You can toggle fDrawUsingShader to create an instance of a shader (as seen in the body of the constructor). After that it adds some initial values to the four arrays fAmbient , fDiffuse , fSpecular , and fShininess .